Simple editor

HTML

<textarea id="editor" onkeyup="sendCode(event)"></textarea>	

<div id="output"></div>

CSS

#output {
    width:200px;
    height:200px;
    background:yellow;
}

JavaScript

var editor = document.getElementById("editor");
var output = document.getElementById("output");
editor.value = "Type here!"

function sendCode(event){

 output.innerHTML = editor.value;
}